package com.itheima;

public class TestDemo12 {
    public static void main(String[] args) {
        String st = "java";
        st = st.concat("world");
        String st1 = st +"world";
        System.out.println(st1);
        st1 =  st1.replace("java","****");
        StringBuilder sb = new StringBuilder(st1);
        sb.append("world").append(11).append('a').reverse().toString();
        System.out.println(sb);
    }
}
